1. Technical Field
The disclosure relates generally to integrated circuit (IC) chip packaging and testing, and more particularly, to a liquid thermal interface and related method.
2. Background Art
During integrated circuit (IC) chip fabrication and packaging, IC chips are tested and burned in at high power to determine whether they perform as required. The high power testing results in the IC chip being exposed to high temperatures. As IC chip feature sizes have continually decreased, more power is required for driving a unit area of silicon (Si) devices, resulting in more heat generation. In addition, higher burn-in powers result in heat gradients (e.g., of up to 50° C.) across the IC chip.
The burn in testing tool comprises a test socket and heat sink as well as related mechanical structures and electronics. During burn-in testing, the tester heat sink is thermally coupled to the IC chip to dissipate heat. Previous generations of IC chips were burned in using heat sinks that were coated with a flat, soft alloy to improve thermal contact. Helium may have also been injected into the interface between the IC chip and heat sink to improve the thermal interface because helium has a better thermal conductivity than air. The advantage of the dry helium interface is the heat sink is easily removed from the chip when burn-in is complete. A dry interface for burn-in testing, however, is inadequate for future IC chips due to the increased heat generation. PAO oil has been used as a liquid thermal interface (LTI) to increase heat transfer. However, PAO oils can degrade at the high temperatures and long times necessary for burn-in testing. Water based fluids have been used as LTI in test; they have excellent thermal performance but are not suitable for high temperatures and can cause corrosion of sensitive devices. Improved LTI is also needed in the final package between the IC chip and lid or between the lid and heat sink.
When the heat sink is pressed into contact with the chip with a force there will generally be a few actual points of contact. The remainder of the area will have a gap which is defined by the flatness of the two surfaces and the force applied. The average thickness of the gap may be on order of 2 microns if great care is taken in the manufacture of the chip and heat sink. The LTI fills these gaps resulting in improved contact between the chip and heat sink. LTIs can be used to thermally couple any two surfaces, for example, heat exchangers or engine components.